[DUBBED VER. REVIEW, no spoilers]
Hey Nana... do you remember the first time we met? You don't? That's OK, because Junko has recaps!
Welcome to Junko's Place, where there is no fourth wall, so the characters are free to talk about the anime that they are in. This is how I describe the "premise" used to present the Nana Recaps. It's great and I will tell you why, but first let me break down the obvious bits.
Oh, and from now on, when i say Nana, I mean the anime, not a person.

Story 5/10: Watching the Recaps at the wrong times will spoil Nana, so be careful! Watch
#1 after episode 11, #2 after episode 21, and #3 after episode 36. The Recaps have no story of their own, but they summarize the incredible story of Nana, at least up to episode 36.

Art 9/10: The art here is the same quality as the show. It's very detailed and has awesome character design and wardrobe. It stands the test of time well (I'm writing this 12 years after the series aired).

Sound 10/10: Viz Media did a top-notch job on the dub. The badass music of BlaSt and Trapnest is here in the Recaps, too.

Character 8/10: You know the characters from the show, so I don't need to tell you about their realism, lovableness, etc. In between recap clips, there are some fun moments with supporting characters. I would have appreciated some of the main characters showing up at Junko's Place, though.

Enjoyment 7/10: We just saw the parts of the show we see in these recaps, so they are not as entertaining as before. The parts between clips, in Junko's Place, are funny and interesting, though.

Overall 8/10: It's so cool to see the characters in the anime talking to the audience and each other about their roles, the other characters, and the recent events as if they have been watching the show, too! Also, I factor into the total score how helpful these Recaps are. Nana is often subtle and there is always a lot going on, so recaps can be helpful to remind you of little things.

TL;DR: These are easily the best "summary" episodes I have ever seen. They have good original content and do a decent job of recapping.
Please be sure to rate this anime after you finish it and thanks for reading my first review!